Electromagnetic relays are well known and have found a variety of useful applications as switching devices. A typical relay is mounted on a base and consists of a frame, a coil assembly consisting of a bobbin with a coil circumferentially wound around the bobbin, a core concentrically located within the coil assembly, a spring-loaded armature assembly, and two electrical contacts, one on the armature assembly and one secured to either the base or bobbin. A relay performs its switching function when the coil is energized, creating a magnetic field which closes the gap between the armature assembly and the core, causing the contact on the armature assembly to make with the contact on the base or bobbin and thereby closing an electrical circuit. When the coil is de-energized the armature assembly springs back to its initial position, the contacts separate and the circuit is opened.
Relative positioning of the various components of a relay is vital to its proper functioning and must be taken into account in order to optimally design a relay. More specifically, the positioning of the core relative to the armature assembly must be precise in order to ensure that the contacts make, and the circuit closes, when the coil is energized and that the contacts separate, and the circuit opens, when the coil is de-energized. Generally the core is positioned with a specific amount of overtravel so that there is sufficient contact force between the contacts to pass electricity efficiently, with the required amount of overtravel being dependant on the specific relay design. Unfortunately, manufacturing tolerances have made the precise positioning of the core difficult to achieve in practice and this has lead to a higher manufacturing rejection rate for relays than is desired.
Understandably, the process of manufacturing relays has been an area of much activity. Recent techniques, as described in U.S. Pat. No. 4,596,972 and 4,749,977, have focused on positioning the core during fabrication of a relay by aligning the core head with the pivot point of the armature assembly. The core head is also used to secure the bobbin into position by having the core head press down on crush ribs attached to the bobbin. Crush ribs are necessary to decrease the likelihood of deformation of the bobbin which, if this occurred, could alter the position of the contact mounted on the bobbin. After this alignment the remainder of the relay is assembled (including armature and contacts). While this design may be an improvement over previous designs, it still allows for errors due to manufacturing tolerances of the armature assembly and any manufacturing tolerance errors introduced during the assembling of the remainder of the relay. A post-assembly measurement of relative positions of the components is then required in order to assure proper functioning. If a relay does not function properly corrective measures must be taken, such as attempting to reposition the contacts or machining of the core. If the corrective measures are insufficient the relay must be scrapped.